Transient grating measurements of film thickness in multilayer metal films

Abstract

A transient grating technique has been used to measure film thicknesses in five multilayer film structures. Through-plane acoustic responses are observed through time-resolved diffraction that reveals their return to the free surface after partial reflections within the structure. Optical heterodyne detection with a controlled reference field amplitude permits optimization of the signal/ noise ratio relative to detection of the signal against the far stronger incident probe field or against a dark background ͑homodyne detection͒. In-plane acoustic waves are also generated and observed.

Crossing disciplines ‐ A view on two‐dimensional optical spectroscopy

“…The spacing of this interference fringe is typically several micrometers, and photographs of the grating are available . The periodicity of the fringe is given by where λ is the excitation wavelength and θ is the crossing angle between the two pump beams . This interference pattern is imprinted, or ‘written’, into the sample when the electromagnetic field interacts with the bound electrons of the material to induce a spatially periodic polarization.…”

Laser-based measurement of elastic and mechanical properties of layered polycrystalline silicon structures with projection masks

“…Ultrasound techniques, using lasers to generate and detect surface acoustic waves ͑SAWs͒, provide a versatile tool to determine simultaneously several unknown film properties. 4,5 A less sophisticated method to generate illuminated periodic patterns at surfaces with a laser can be realized with a projection mask. 2 On the other hand, frequencies up to a few gigahertz have been realized with the transient lasergrating technique, where two temporally coincident picosecond laser pulses are crossed at the sample surface, giving rise to interference patterns with spatially periodic heating and expansion that launch two counterpropagating narrowband acoustic wave trains.…”

Imaging of transient surface acoustic waves by full-field photorefractive interferometry

“…7,8 Optical detection of SAW induced displacements at a single location can be done with high sensitivity, e.g., by interferometric detection, 9,10 laser beam deflection, 11,12 modulated optical reflection, 13 or heterodyne diffraction detection. 14 Single SAW signals contain valuable information on the SAW velocity and attenuation, which are related to the elasticity and microstructure of the materials. 6,9,12,15,16 By analyzing signal contributions due to SAW mode conversion at defect related elastic discontinuities along the path between the excitation a) Authors to whom correspondence should be addressed.…”